The present invention relates generally to multicasting. More particularly, the invention relates to a dual encryption protocol for scalable secure group communication.
With the widespread use of the Internet, securing data transmissions is an important requirement for many applications. Several protocols exist to address security in data networks with respect to unicasting. Unfortunately, these protocols cannot be easily extended to protect multicast data.
Multicasting poses several problems that do not come up in securing unicast data transfers. First, multicast addresses are not private, which enables any interested host to join the multicast session without any hindrance. Next, multicast data is transmitted over many channels of the network, which presents multiple opportunities for attacks such as eavesdropping. Furthermore, any host in the Internet can send irrelevant data to the multicast group, which may cause congestion. The universal knowledge of multicast addresses also allows any host to pose as a member of the group, thereby allowing it to gain access to the multicast data. Finally, adversaries can possibly disrupt the multicast protocol itself by posing as legitimate members of the group.
Multicasting is a scalable way of transmitting data to a group hosts and any secure multicasting protocol must be scalable as well. A secure group communication protocol should provide group membership control, secure key distribution, and secure data transfer. If the multicast group membership is dynamic, i.e., if the group members join and leave during the course of a multicast session, the secret keys need to be updated accordingly. In other words, members of a multicast session must not be able to access the multicast data transmitted before their membership has begun or after their membership has expired. Scalability in this context implies that the overhead involved in key updates, data transmission and encryption must be independent of the size of the multicast group. The other requirement of scalability is that the addition or removal of a host from the group should not affect all the members of the group. The second rule is called "1 affects n" scalability problem.
Several protocols have been proposed to support secure multicasting. Based on the corresponding key distribution protocols, we can broadly classify them into three categories, viz., centralized flat schemes, distributed flat schemes and hierarchical schemes.
Centralized flat schemes consist of a single entity distributing the encryption keys to the group members. On each membership change the group manager securely transmits updated key(s) to all the members. Thus these schemes suffer from the 1 affects n scalability problem.
Distributed flat schemes trust all the group members equally. Members joining early create and distribute the encryption keys. Trusting all the members makes this protocol vulnerable to security attacks from inside the group.
Hierarchical schemes distribute encryption keys via a distribution tree. Two classes of hierarchical protocols have been proposed. The first class uses a hierarchy of keys while the second group uses a hierarchy of nodes to achieve scalability.
Hierarchical key based schemes suffer from the 1 affects n scalability problem. Typical hierarchical node schemes entrust internal nodes of the key-distribution tree with the distribution of the encryption keys. But they offer no mechanism to hide secure multicast data from the internal nodes.
The present invention proposes a dual encryption protocol (DEP) for scalable secure multicasting which supports one-to-many group communication. The invention uses hierarchical subgrouping of multicast members to address scalability. Each subgroup is managed by a subgroup manager (SGM) which assists in key distribution as well as group access control. The protocol also distinguishes between participants and members of the multicast group. Members of the multicast group are leaf nodes and internal nodes (SGMs) in the key distribution tree, that are entitled to the multicast data. On the other hand, participants of the multicast group are SGMs that assist in enforcing the secure multicast protocol without having any access to the multicast data. The dual encryption scheme enables the protocol to hide multicast data from the participants.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.